The specific aims of this subproject are to: 1. Determine the baseline levels of the subgingival microbiota in the in the HIV-negative and HIV- positive IVDU; 2. Investigate the microbial etiology of HIV-associated periodontal diseases in the IVDU population; 3. assess the baseline subgingival plaque microbiota in HIV-positive and HIV-negative children, and; 4. Assess the cross-sectional relationship between the presence of specific microorganisms with regard to the clinical expression of HIV- associated periodontal lesions and the immunological status of the HIV- seropositive subject (as assessed by T4 cell number). We hypothesize that the baseline subgingival microbiota of the HIV- infected individual may be different from the HIV negative individual because of the consequence of HIV-infection (decreased host defenses). We further suspect that these changes will become greater as the immunocompetence of the subject becomes further impaired (specifically T4 cell number). With regard to the etiology of HIV-periodontitis, we hypothesize that: the HIV-seropositive patient may be susceptible to infections by opportunistic organisms not commonly inhabiting the mouth and/or the normal periodontopathic microbiota overwhelms the crippled immune system of the HIV-seropositive patient. Finally, we expect to see similar changes in the children. Specifically, those children with HIV- periodontitis will harbor a periodontopathic/opportunistic microbiota more typical of an adult rather than child.